Wireless duplex signaling system



May'. 6 1924. ,493,51 y v M. M. DOLMAGE 4 WIRELESS DUPLEX SIGNALING SYSTEM Filed Sept. 17. 1920 INVEN'DOR 7;

f voice Patented May l 6, 1924.

artr- MII-IRAN M. IDOLMAGE, OF WASHINGTON, DISTRICT 0F CLTJ'IIttBIA.v

WIRELESS DUPLEX SIGNALING SYSTEM.

Application led September 17, 1920. Serial No. 410,929.y

T0 @ZZ Awhom t ymay,conce/rn Bc it known that I, MIHRAN M. DOLMAGE, a citizen of the United States, residing at 825 Vermont Avenue, ld/vashington, in the District of Columbia,have invented certain new and useful Improvements in a Wireless Duplex Signaling System, of which the following is a specification.

This invention relates to a system for the transmission and reception of wireless signals.

This invention utilizes for this purpose operated circuit changing means which control the circuits of the two-way wireless system in such a way as to completely eliminate the reaction of the transmitted energy upon the receiving apparatus at the transmitting station. Circuit changing means, voice controlled in their operation have heretofore been disclosed. This invention differs however from most previous inventions in that it does not require the operation of a switch for putting the transmitting apparatus into electrical connection with the antenna. In the system described herein, the transmitting apparatus as well as the receiving apparatus at the wireless station are normally connected to the antenna. No part of a sentence spoken into the transmitter at the wireless station is distorted or lost during the time interval required for establishing a condition for proper transmission, as inthe systems previously disclosed by other inventors utilizing normally open transmitting circuits in combination with voice controlled means for closing the transmitting circuits to the antenna.

In radio telephony it has been customary to supply to the antenna a wave of constant frequency and constant amplitude by means of a sending generator. The amplitude of this wave is then modulated in accordance with the signal to be sent. t

It is well known that when a constant amplitude wave of frequency C (carrier wave) is modulated by means of another constant amplitude wave of low frequency S (signal wave), the resultant modulated wave can be considered to be made up of waves of constant amplitudes and of frequencies (S), (C), (G+S) and (C-S).

In Patent No. 1,414,629 I disclosed a system wherein the modulated wave comprising the waves of the frequencies (C-l-S),

(C-VS) and (C) s impressed upon the grid C), C-S). The wave of signal frequency S) thus obtained is then usedy tosecure the i ope-ration of'a suitably designed control relay, responsive to currents of frequency (S). In the present invention a system is used to achieve the same purpose in a different way,

which avoids the need .for a detecting tube as hereinabove described, by separating through properly tuned circuits, the waves (S), (G+S), (C) and (C-S), produced by t-he modulating action of the signal wave (S) upon carrier wave (C), into two groups. The first group, consisting of a signal wave (S) is used to operate the circuit changing means and a second grou consisting of the waves (C-i-S), (C), (C'-S) is allowed to be radiated by the antenna. invention, remains unoperated, when no modulating signal wave is present, as all currents of carrier y frequency have been filtered out. y

An important advantage of Ithe system described herein consistsin the possibility it It is obvious that false operations would result if no provision was made for such shielding. f

In the invention herein disclosed the` The control relay, in the presenty voice operated relay which controls the re- 'i ception of signals is connected to points ofthe same potential under all conditions, for

The

in the accompanying drawingsv in which carrying out the invention.

Figure 1 indicates the general method of Figure 2 indicates a modification of detailin the arrangement shown in Figure 1. this modification including the insertion of an amplifier for purposes `of more certain control. in Figure 3 is shown a further modification of detail,the means required to enable the use of a direc-t current control relay instead of an alternating current control relay. Figure 4 is a still further modification, also of detail, which may be used in conjunction with any of the `arrangements shown on Figures 1, 2 or 3, consisting of a more efficient ilter for the elimination of radio frequency currents.

.This invention is illustrated in. its fundamental features in Figure 1. Referring to this figure. 1 is an antenna for the transmission and the reception of signal/s. Autenna 1 includes tivo parallel branches which are also in series with the vprimary of receiving transformer V19. One branch. includesprimary winding of transformer coil 2, of controlling` circuit A and secondary Winding of transformer The other branch includes primary Winding oftrans former coil 3, of automatic controlling` circuit A and anartilicial line comprising inductive resistance 4. and condenser 5. lt is contemplated to have the artificial line balance` very accurately the transmitting circuit of the duplex system. This arrangement neutralizes'completely the electromotiveforces generated in the secondary windings of coils 2 and 3, on all vreceived signals. Transformer 6 is connected to the plate circuit of a vacuum tube modulator 7. rlhe grid circuit of the same tube 7 is'connected to condenser 8 which in turn is bridged by modulating transformer 9 and output Winding of transformer 11. rllhe primary Windingof transformer 11 is connected to suitable source 12 of carrier currents. rllhe secondary windings of coils 2 and 3 are closed throughvariable condenserI 13 and inductance 14. rlhe capacity of condenser 13 is so adiusted as ,to result in a resonance condition for the signaliwaves as described subsequently in greater detail in these specifications. Bridged around con-- denser 13 is control relayA 18.

ln Fi gure 2. an amplifier 15 is introduced between relay 18 and variable condenser 13 of Fig. 1, to secure a more certain operation .of relay 18, in case the relay available for use as control relay is not sufficiently sensitive. In Fig. 2 the grid circuit of amplifier 155s bridged around variable condenser 13. The plate circuit of the amplifier is closed through a resistance 16. Bridged around this resistance is the series combination of condenser 17 and relay 18. Condenser 17 is adjusted so as to secure resonance conditions for currents of signal frequency. ln

Fig-3, is shown an alternative arrangement to that shown on Fig. 2. ln this figure the grid circuit of a vacuum tube 15 is again bridged around condenser 13. The plate circuit of this tube is closed through direct current relay 29, which is bridged by condenser 28 to allow the fiovv of alternating currents in the plate circuit. To prevent relay 29 from being continuously operated by the plate current a direct current counter electromotive force is applied through variable resistance 30 across the windings of relav 29.y in this arrangement the potential of the grid battery of the vacuum tube 15 is adjusted so as to have this tube act as a detector. lVhen alternating cur-y rents of signal frequency are impressed upon the grid circuit of 'vacuum tube 15 the increase in plate current results in the operation of control relay 28. Variable'resistance 30 is normally so adjusted that when no modulating signal Waves are pres ent relav 29 remains unoperative.

ln Fig. 4 is shown an improved arrangement over that shovvuin Fig. 17 as regards the effective timing out of carrier frequency currents from the circuit of condenser 13. ln this figure the circuit of the secondary windings of coils 2 and 3 `is closed through anti-resonant device 31 and series resonant combination 32. Around combisol nation 32 is bridged a second anti-resonant to carrier frequency (C) and very approxi-y mately resonant to carrier frequencyy (C-S) and (C-l-S). Variable condenser 13 is adjusted as in Fig. l, to secure resonant conditions: for currents of signal frequency (S). it will be readily understood that the combination of elements 31, 32,'and is essentially a filter for carrierfrequency Waves Which prevents these Waves from reaching condenser 13. Referring to the circuit shown on Fig. '1, the following operation Would obtain. Carrier frequency currents generated by source 12 are amp-lified by modulating tubc 7 and transmitted through transformer 6 and coil 2 to the an* tenna. rfhesc carrier frequency currents include the Waves (G+S). (C) and (Cl-S). The combination of condenser 13 and inductance 14 is so chosen as to offer a very lll) pressed upon the grid circuit of tube 7, these currents, amplified by tube 7, flow through transformer 6, primary windings of coils 2 and 3 and balancing impedance having elements 4f and 5. The secondaries of coils 2 and 3 are so connected that the electromotive forces induced are cumulative. Since, in addition, the condenser 13 and inductance 14 forms a resonant combination to currents of signal frequency such currents will flow freely in the auxiliary circuit and operate relay 18. Vhen operated, this relay short circuits tuning condenser 23, thereby preventing any of the transmitted modulated waves (C), (G+S), (C-S) from producing audible signals in receiver 27. This receiver remains, therefore, absolutely silent. i

However, on signals received by the anten-v na, on account of the electrical association of coils 2 and 3, in the manner shown and as previously described, the two terminals of condenser 13 will .be at the same potential. This result follows, since by construction, on received signals the electrical impedance of artificial balancing circuit, comprising elements 3, L and 5, is equal to the impedances of the transmitting circuit comprising elements 2 and 6. The electromotive forces generated in the secondarie-S of coils 2 and 3 will consequently be equal and opposite in phase. Hence, no current flows in the circuit .of secondaries of coils 2 and `3, on received signals, whether such received signals be due to carrier frequency waves from other transmitted stations, static impulses or grinders. No current can therefore flow through relay 18. This relay remains in its non-operated position on all signals received by the antenna.' The carrier frequency currents flowing through transformer 19 on received signals will therefore reach their destination unhampered and the receiving will be obtained in full amplitude at receiver 27. The modification shown on Fig. 2 is merely for the purpose of securing increased certainty of operation as already described, when large currents are required to operate control relay 18. Further modification shown on Fig. 3, furnishes a rather convenient meansfor using a direct current relay instead of an alternating current relay. 4Vith this arrangement the tuning of the auxiliary circuit need not be very close since the effect of the increase in plate current, due to carrier frequency waves, can be eliminated to anyhdegreev desired by the regulation of the counter electromotive battery through the variation of adjustable re-` sistance 30. y .The improved arrangement shown on Fig. LLean be used in combination with any one of the arrangements shown on Fig. 1, Fig. 2 or Fig. 3. It may not, at first sight, be immediately clear that it is possible to tune the auxiliary circuit A of the present invention to currents of signal frehas already been tuned .to currents of carrier' frequency. This result is a typical `consequence of the special arrangement indicated on the drawings of this invention and may y be demonstrated very clearly as shown hereunder. Referring to Fig. l of the drawings and calling- Y i v .l

EzElectromotive force of the transmitted waves acting through the back impedance of the transmittingequipment.

Z,:Impedance of the transmitting equipment. l

It will be remembered in vthis connection that elements 4 and 5 balance exactly the tranmitting equipment, as brought out on page 3 ofthe specifications, lines y17 to 19,

andr therefore have the same total impedance. y

Zszlfmpedance of the secondary windings of coils 2 and 3.

Zgzlmpedance of the primary windings of coils 2 and 3 which are directly in series with elements 41, 5, and 6. Y l ZlzImpedance of the` antenna c circuit, including that of element 19 with associated receiving equipment closed through.

Z-:Impedance of condenser 13. i PMzMutual impedance of primary' and secondary windings of coils 2 and 3 for frequency 27ri IlzCurrent in antenna circuit. ISI-Current in. auxiliary circuit.y lzCurrent in balancing elements 4 and 5. Il-i-LzTotal current flowing through element 6.

Wel may write the three following equalar terms containing the same ,currents and solving for I1 and I3, weiget- Considering first the expression for the antenna current it is clear that it depends upon the three inipedances Z2 Z,c and?1 but in no Way upon Z or Z3. The antenna circuit may therefore be tuned in the usual Way for resonance to carrier frequency currents, independently of the value of Z.

Considering next the expression for the current in the auxiliary circuit it Will be noted that it depends upon the five impedances PM, Z2, Z4, Z3, and Z. It Will also be noted that this current does not depend upon Z1, the impedance of the antenna circuit. The impedance Z of condenser 13 may therefore be chosen so as to secure maximum current conditions for the audio frequency components of the electromotive force E, Without in any manner interfering with the securing of resonance conditions in the antenna for radio frequency currents.

It is clear from the above description that this invention is not in any Way .limited to any one particular type of Wireless signalling system. What is characteristic of the system is the use of an auxiliaryy circuit tuned to currents of signal frequency, an antenna circuit tuned to-carrier frequency, of a control relay in this auxiliary circuit actuated by currents of signal frequency, with balancing artificial network, substantially as described. Instead of using a control relay of alternating current type, I find it desirable in some cases, to use a direct current relay in association with a counterbalancing electrometive force, this combination taking the place of the alternating current relay 18 and cond enser 17.

What I claim is 1 1. In a system for the transmission and reception of Wireless signals, transmitting apparatus normally connected to the antenna receiving apparatus normally connected to the antenna, an auxiliary circuit tuned to currents of signal frequency, a control relay in said circuit and circuit changing means under the control of aforesaid relay rendering inoperative the receiving apparatus when said system is used for transmission.

2. In a system for the transmission and reception of Wireless signals, an antenna, transmitting apparatus normally connected to said antenna, an auxiliary circuit tuned to currents of signal frequency, a second circuit balancing the transmitting circuit on received signals, a control relay in said auxiliary-circuit and means under the control of aforesaid relay rendering the receiving circuit inoperative When said system is used for transmission.

3. In a system for the transmission and reception of Wireless signals, an antenna, transmitting apparatus normally connected to the antenna, an auxiliary circuit tuned to currents of signal frequency, a second circuit balancing the transmitting circuit on received signals, means for connecting said auxiliary circuit With said transmitting circuit and said balancing circuit, a control relay connected to points of equal potential for received energy in aforesaid auxiliary circuit, receiving apparatus normally connected to the antenna, and means under the control of aforesaid relay rendering inoperative the receiving apparatus When said system is used for transmission.

4. In a system for the transmission and reception of Wireless signals, the combination of an antenna, transmitting apparatus, and an auxiliary circuit-these elements Wired in a bridge arrangement With the antenna and auxiliary circuit occupying opposite arms of the bridge, With voice controlled circuit changing means-in said auxiliary circuit completely shielded from all interfering Waves received through the antenna.

5. In a system for the transmission and reception yof `Wireless signals, amodulating device, the bridge combination of an antenna, transmitting apparatus and an auxiliary circuit, the antenna and the auxiliary occupying opposite arms of said bridge, receiving apparatus, and circuit changing means controlled by signaling currentsrendering` inoperative the receiving apparatus when said system is used for transmission.

6. In a system for the transmission and reception of Wireless signals, an antenna, transmitting apparatus, receiving apparatus, an auxiliary circuit, means for filtering out currents of carrier frequency from said auxiliary circuit, a control relay in said circuit and means under the control of said relay rendering inoperative the receiving apparatus when said system is used for transmission.

7. In a system for the transmission and reception of Wireless signals, the combination of an antenna, transmitting apparatus and an auxiliary circuit in bridge arrangement, a control relay connected to points of equal potential for received signals in said bridge, means for preventing the 'flow of transmitted carrier currents through said relay, and means under the control of said relay rendering inoperative the receiving apparatus when said system is used for transmission.

In testimony whereof I ax my signature.

lun-IRAN M. DoLMAGE.

In presence of- MALLEN GORE RICHARDSON, ROBT. E. P. KREITER. 

